/*
 * nimbus-jose-jwt
 *
 * Copyright 2012-2016, Connect2id Ltd.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use
 * this file except in compliance with the License. You may obtain a copy of the
 * License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed
 * under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
 * CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 */

package org.ovirt.engine.core.sso.api.jwk;

import java.math.BigInteger;

/**
 * Big integer utilities.
 *
 * @author Vladimir Dzhuvinov
 * @version 2013-03-21
 */
// copied from nimbus-jose-jwt version 8.2
public class BigIntegerUtils {

    /**
     * Prevents public instantiation.
     */
    private BigIntegerUtils() {

    }

    /**
     * Returns a byte array representation of the specified big integer without the sign bit.
     *
     * @param bigInt
     *            The big integer to be converted. Must not be {@code null}.
     *
     * @return A byte array representation of the big integer, without the sign bit.
     */
    public static byte[] toBytesUnsigned(final BigInteger bigInt) {

        // Copied from Apache Commons Codec 1.8

        int bitlen = bigInt.bitLength();

        // round bitlen
        bitlen = ((bitlen + 7) >> 3) << 3;
        final byte[] bigBytes = bigInt.toByteArray();

        if ((bigInt.bitLength() % 8) != 0 && ((bigInt.bitLength() / 8) + 1) == (bitlen / 8)) {

            return bigBytes;

        }

        // set up params for copying everything but sign bit
        int startSrc = 0;
        int len = bigBytes.length;

        // if bigInt is exactly byte-aligned, just skip signbit in copy
        if ((bigInt.bitLength() % 8) == 0) {

            startSrc = 1;
            len--;
        }

        final int startDst = bitlen / 8 - len; // to pad w/ nulls as per spec
        final byte[] resizedBytes = new byte[bitlen / 8];
        System.arraycopy(bigBytes, startSrc, resizedBytes, startDst, len);
        return resizedBytes;
    }
}
